How are precise patterns of synaptic connections formed during the development of a nervous system? Establishment of these patterns require both neuronal activity-dependent and activity-independent mechanisms. It is clear that axons stop growing in response to signals from their targets (and sometimes other cells), but it is not clear what those signals are or how they are generated. C.elegans is a model organism in which to study this phenomenon because of its powerful genetics and extremely well characterized nervous system. Recently, three genes were cloned which specifically affect the axon migration and termination of one chemosensory neuron, ASJ. The identity of these genes led to the proposal that cGMP signalling plays an important role in the proper guidance and termination of this axon. The first aim of this proposal is to determine what role electrical activity, synaptic transmission, , and the targets of ASJ have on the migration and termination of its axon, as well as to investigate the functional importance of cGMP signalling in axon migration. The second aim of this proposal is to isolate and characterize novel genes required for ASJ guidance through a visual genetic screen.